Hexafluoroisobutylene's utility is shown by the variety of fluoromonomers and hydrocarbon monomers with which it copolymerizes. For example, it copolymerizes with vinylidene fluoride (U.S. Pat. No. 3,706,723), with vinyl fluoride (International Application WO 2001-037043), with ethylene and tetrafluoroethylene or chlorotrifluoroethylene (European Patent No. 0 121 073 B1), with trifluoroethylene (International Application WO 2001-037043), and with tetrafluoroethylene and vinyl acetate (European Patent No. 1 169 399 A2). Its utility as a component of polymers could be increased if means could be found to add substituents to it. For example, if hexafluoroisobutylene could be substituted to provide functional groups such as acids, the monomer could be used in making fluorinated ion-exchange polymers.